This invention relates to devices for measuring soft contact lenses and, more particularly, to devices for measuring the powers and axes of toric soft contact lenses. The invention also permits inspection of the lenses for defects.
It is common practice to verify the lens strength of spectacle lenses and rigid contact lenses prior to dispensing the lenses to the patient. Although soft contact lens prescriptions are equally as important, it is accepted practice to dispense soft lenses to the patient without verifying the accuracy of the prescription. Soft lenses are not verified because of the difficulties involved in the procedures used at this time.
The current procedure for measuring soft lens power involves first blotting the lens to remove excess surface saline. The lens is then picked up with a tweezers or the fingertips, and then placed on the lens rest of an instrument. Proper placement of the lens is difficult because of the wet, sticky surface of the lens and its floppy consistency. If the lens is improperly placed on the lens rest it must be lifted off and repositioned. At times the lens is properly positioned, but the reading must be repeated due to uneven surface wetness. However, the lens must be checked quickly because the instrument reading will be wrong if the lens dries too much. If it becomes too dry, it must be rehydrated for several minutes before retesting is attempted. After the reading is completed, the lens is removed from the lens rest and returned to its vial. At this point, lifting the lens requires great care with some instruments due to the strong tendency of the lens to cling. Unfortunately, this type of handling can damage a soft lens. The lens is also prone to contamination from the lens rest.
In addition to the above difficulties, measuring toric soft lenses presents further problems. The markings on the lenses must be properly oriented as the lens is placed on the instrument so that the lens axis can be accurately read. The markings are very faint, making them difficult to see when positioning the lens on the instrument lens rest. Also, the markings themselves must be verified.
Several attempts have been made over the years to facilitate making lens power measurements. Wet cells, such as in U.S. Pat. Nos. 3,779,648; 4,277,172; 4,415,076; and 4,496,243 have not come into common use because of the poor accuracy resulting from measuring lens power in saline as opposed to measuring lens power in air. Also, these devices do not aid in orienting toric lenses for axis measurements.
U.S. Pat. No. 3,820,899, issued June 24, 1974, discloses a device for holding soft contact lenses for inspection. As in the previously cited patents, this device fails to address the problem of rotational orientation of toric lenses. Further, the black plexiglass suggested in the patent would make visualization of the lens markings difficult due to the opacity of the material, although the flange configuration required would tend to obscure the markings even if a transparent material were to be used. Although the patent discusses the need for minimizing the vertex distance of the lens, the device creates a vertex distance which would affect measurements of strong lenses adversely. The device described is limited to measurements of front vertex power, whereas many contact lens manufacturers use the back vertex method of measurement.
U.S. Pat. No. 4,072,428, issued Feb. 7, 1978, also discloses a device for holding soft contact lenses. This patent also fails to address the problem of toric lens orientation. The translucent white plastic suggested in the patent would interfere with visualizing the reference markings of the lens. This device is not capable of measuring the front vertex power of lenses being tested, even though several manufacturers measure their lenses by the front vertex method. An additional problem created by this device is the great degree of adhesion of the wet, sticky lens to the described hemisphere due to the intentional close match of lens and hemisphere curvatures. Removing the lens from the hemisphere would require a great amount of care and might result in damage to the lens.